The present invention relates to a dot impact type serial printer applicable to, for example, a computer output terminal.
It is a common practice with a conventional dot impact type serial printer to arrange the tips of print wires in a single array or in two or three parallel arrays. Selected print wires in the same array which match a desired print pattern are driven at the same time to impact against a platen.
Since the selected wires of each array impact against the platen at the same time, the surface of the platen is elastically deformed to a noticeable extent. Such deformations of the platen are sequentially propagated along the platen to produce surface waves having various frequency components. The surface waves are repetitively reflected at the ends of the platen and propagated back and forth along the surface of the platen. While the surface waves are so propagated back and forth, a standing wave, having the same period as the time in which the surface wave passes along the length of the platen, is generated in the surface of the platen.
The dot impact type serial printer continuously impacts the print wires thereof against the platen at a predetermined period. Hence, the surface waves are continuously generated and, when the impacting period is identical with the period of the standing wave, the surface waves cooperate with the standing wave. In this case, surface oscillation is stably occurred on the surface of the platen. Such surface oscillation constitutes the source of unpleasant noise.